1918 | Taylor: Revision of the Rodent Genus Aplodontia 44] 
in diameter, which stands out in strong contrast to the grayish or 
weakly brownish coloration of the underparts. In males and in 
ce 
winter females the ‘‘spot marks’’ are inconspicuous or lacking. 
It would be difficult, if not impossible, to determine the sex of the 
individual in any given instance by study of the cranium. There is 
a tendency for ridges and processes to be somewhat more accentuated 
in the males, for zygomatic arches to be somewhat heavier, and for 
the temporal ridges to be more closely approximated. Usually the 
males have basilar length, zygomatic width, mastoid width, and dis- 
tance transversely across the angular process of the mandible greater 
than in the females. The largest, heaviest specimens in any adequate 
series of skulls are usually those of males. In Aplodontia rufa 
olympica the range of variation in size is greater, on the basis of the 
specimens measured, in the males than in the females. In certain 
forms the females have the alveolar length of the superior cheek teeth 
greater than in the males, though the measurements of the latter may 
exceed those of the former in most respects. In at least two forms, 
on the basis of measurements taken, the females have interpterygoid 
fossae averaging broader than in the males. In practically all 
instances, however, the range of individual variation is so great as 
to transeend that due to sex. 
3. INDIVIDUAL VARIATION 
While in the present study it has been impossible to eliminate 
geographic, sex, and age variation altogether, still it is believed that 
the observations, measurements, and percentages given are of value, 
sinee they suggest the range of variation, chiefly individual, which 
must be reckoned with in using a typical series of adults in specifie 
comparisons. 
In a series of eleven specimens of Aplodontia rufa pacifica taken 
in February, March and April, there is but little variation in color. 
Dorsally and laterally all are grizzled pinkish cinnamon, with the 
brown coloration a little more intense in certain specimens, a little 
less so in others. The brown wash ventrally varies from near hight 
pinkish cinnamon to pinkish buff. A little more variation, however, is 
apparent in twelve examples taken during October, November and 
December. The dorsal coloration in these varies from cinnamon or 
sayal brown to pinkish cinnamon or light pinkish cinnamon. The 
pelage of one specimen (no. 9077, Field Mus. Nat. Hist.) is in very 
